In copending patent application Ser. No. 555,471 filed Nov. 28, 1983 of Wilhelm BONGARD et al, entitled REMOTE-CONTROLLED LOCK SYSTEM a lock system is described that has a transmitter that can be set to emit any one of a succession of differently coded signals, a receiver that can be set to respond to any one of the succession of signals, and a lock operable by the receiver when it receives the signal it is set to. Initially according to this invention the transmitter is set to emit a predetermined one of the succession of signals and the receiver is set to respond to the predetermined one of the signals. Thereafter, after each emission by the transmitter and reception by the receiver, the transmitter and receiver are reset to the next of the signals in the succession except after the last signal of the succession has been emitted and received in which case the transmitter and receiver are reset to the first of the succession of signals.
The transmitter includes an encoder that can produce an unlocking signal that is constituted by any of a plurality of different main code words, that is the transmitter can emit any of a succession of differently coded signals. This transmitter also includes a resetting unit that automatically advances the transmitter to the next signal of the progression each time it is actuated. When the last signal of the succession is emitted the transmitter is reset to the first of the succession, and the process can be repeated.
The receiver is complementarily constructed so that it can respond to any one of the signals, but is settable to respond only to one of them. A resetting unit in the receiver resets it to the next of the succession of signals each time a signal is successfully received, or to the first of the succession when the last signal of the succession was received. Thus the transmitter and receiver will be indexed synchronously through the succession of signals.
In this manner if a would-be thief or the like monitors the site and is able to receive and duplicate the coded unlocking signal, he or she will not be able to operate the lock, as this particular signal is not going to work again until the entire succession has been generated, which will not be for a long time with a large succession having 10.sup.6 to 10.sup.9 different main code words that themselves follow a random or complex succession. In this manner it is possible to provide such lock systems on an entire series of cars with the likelihood of one transmitter opening another being statistically insignificant. If a code is used having 10.sup.6 to 10.sup.9 main code words, it is possible to use only a portion of the code having 20 to 30 code words, thereby allowing the same equipment to be used while largely eliminating the chance of overlap.
A potential source of difficulty with this arrangement, however, is that the transmitter and receiver can get out of synchronization. This happens when, for instance, the transmitter is actuated while out of range of the receiver, so that the transmitter is stepped to transmit the next word of the progression while the receiver is still only able to respond to the one it missed. This difficulty is overcome in the prior-art system by transmitting an auxiliary or synchronization signal that does not correspond to any of the signals of the succession and simultaneously resetting the transmitter to a predetermined one of the signals of the succession. The auxiliary signal is received and in response thereto the receiver is reset to the predetermined one of the signals of the succession and simultaneously the receiver can open the lock. For maximum security the receiver is only reset to the predetermined one of the signals when it has just received a signal corresponding to one of the signals in the succession that is not the one the receiver is set to.
Thus the transmitter has an additional auxiliary encoder or generator which can be actuated to produce an auxiliary code word which does not correspond to any of the main code words of the acceptable progression. The receiver has an auxiliary decoder or detector which converts the auxiliary code word into the unlocking signal when previously the receiver has received a main code word that is of the acceptable succession but not the one the receiver is currently addressed to. In such a situation both the coder of the transmitter and the decoder of the receiver are reset, normally to the first main code word of the succession.
Such an arrangement provides a high degree of security, but still can be gotten around by a sophisticated thief who sets up a receiver and recorder to monitor the site for a period sufficient to learn the auxiliary code word and the subsequently employed main code word. Such a thief would randomly generate code words until the receiver is tripped or stepped, then would wait for a legitimate user of the system to have to employ the auxiliary code word to reset the system.